1. Field of the Invention
The present invention relates to optical communications systems. More particularly, the present invention relates to regulating and managing the operation of optical networks.
2. Description of the Background Art
A. Optical Communications Systems
Optical communications systems are rapidly becoming a widespread and important technology in telecommunications and networking. Optical communications systems transmit information optically at very high speeds over fiber optics.
The basic components of an optical communications system include: an optical transmitter; fiber optics; and an optical receiver. An optical transmitter incorporates information to be communicated into an optical signal and sends the optical signal. Fiber optics carries the optical signal over a distance. Finally, the optical receiver receives the optical signal and recovers the information therein.
B. Limited Dynamic Range of Optical Receivers
One problem with optical communications systems relates to the limited dynamic range of optical receivers. Optical receivers typically operate properly only within a relatively narrow range of optical signal power levels.
C. Attenuation of the Optical Signal
Another problem in optical communications systems is attenuation of the optical signal. The attenuation may occur due to transmission of the signal, distribution of the signal, and losses due to insertion of components in the transmission path. Optical amplifiers may be used to compensate for signal attenuation. However, conventional optical amplifiers have had various problems.
i Fiber Amplifiers
One type of conventional optical amplifier is a fiber amplifier. A fiber amplifier includes a length of fiber which is doped so that it may form an active gain medium. Ions of rare-earth metals, such as Erbium, are typically used as the dopant.
The doped fiber is pumped so that a population inversion of electronic carriers occurs in the active medium. The pump typically is an optical source whose wavelength is preferentially absorbed by the ions and yet different from the optical signal to be amplified. The optical signal is input from un-doped fiber to the doped fiber, experiences gain due to stimulated emission as it passes through the doped fiber, and then is output in amplified form from the doped fiber to further un-doped fiber.
One problem with fiber amplifiers is the narrow range of wavelengths that they can amplify when multiple fiber amplifiers are cascaded. Another problem with fiber amplifiers is their transient response to channel drop-out in.wavelength division multiplexing systems. Further problems with fiber amplifiers include their relatively large size, slow speed for switching, power inefficiency, difficulties in mass producing them, and their high cost which makes them prohibitively expensive for many applications.
A problem of particular interest with fiber amplifiers is that the gain applied by fiber amplifiers may depend substantially on power levels.
ii. Conventional Semiconductor Optical Amplifiers
Another type of optical amplifier is a conventional semiconductor optical amplifier. Conventional semiconductor optical amplifiers comprise a semiconductor laser like structure which operates below the lasing threshold.
Typically, an electrical current is used to pump the electronic population in the active region of the amplifier. The optical signal is input from fiber optics to the active region of the amplifier, experiences gain due to stimulated emission as it passes through the active region, and is output in amplified form to further fiber optics.
One problem with conventional semiconductor optical amplifiers is that the amount of gain experienced by the input signal is dynamically dependent on the strength of the input signal at a particular instance in time. For instances when the input signal is higher, the signal experiences less gain than for instances when the input signal is lower. This dynamic gain variation is due to gain saturation. Gain saturation occurs when there are insufficient carriers in the conduction band to provide the full amount of gain to the higher signals.
D. Monitoring and Managing the Operation of Optical Networks
A further problem in optical communications systems relates to monitoring and managing the operation of optical networks. Enormous amounts of time and resources are used to build complex optical networks.
Monitoring the operation of such an optical network is needed to quickly and efficiently locate and solve problems (faults) in the optical network. For example, if a user of an optical network reports that his or her connection to a server suddenly dropped, then a network management engineer would want to be able to remotely check the operation at various locations between the user and the server in order to identify and locate the source of the fault.
Regulating the operation of such an optical network is needed to maximize its efficiency and robustness. For example, if optical signal power levels within one area of the network are too low in power, then a network management engineer would want to be able to remotely regulate devices in the network which control the optical signal power levels so as to correct the low power condition.
The problems and disadvantages heretofore associated with the prior art are overcome by the present invention. The present invention provides an optical signal power monitor and regulator. In accordance with a preferred embodiment of this invention the optical signal power monitor and regulator comprises: a lasing semiconductor optical amplifier for receiving the optical signal and whose laser output is used to monitor a power level of the optical signal; a monitor circuit which receives the laser output and outputs a monitoring signal; a tunable element for receiving a version of the optical signal and whose level of amplification is adjustable and for outputting an amplified optical signal; and a regulator circuit for receiving the monitoring signal and adjusting the amplification of the tunable optical amplifier depending upon the monitoring signal. Further in accordance with a preferred embodiment of the present invention, the tunable element comprises a tunable gain-clamped semiconductor optical amplifier. Such an embodiment is capable of automatically regulating the tunable element such that a power level of the amplified optical signal is kept stable. In addition, in accordance with a preferred embodiment of the present invention, the monitor circuit may be used to send status information regarding the optical signal to a network management system, which in turn may send to the regulator circuit a managing signal affecting the level of amplification to be applied to the optical signal.